This invention relates to a process and an apparatus for generating images in real time, and more particularly to a process and apparatus for printing a postage indicia on a column-by-column basis in real time.
Traditional postage meters imprint an indicia on a mailpiece as evidence that postage has been paid. These traditional postage meters create the indicia using a platen or a rotary drum which are moved into contact with the mailpiece to imprint the indicia thereon. While traditional postage meters have performed admirably over time, they are limited by the fact that if the indicia image significantly changes, a new platen or rotary drum will have to be produced and placed in each meter. Accordingly, newer postage meters now take advantage of modern digital printing technology to overcome the deficiencies of traditional meters. The advantage of digital printing technology is that since the digital printhead is software driven, all that is required to change an indicia image is new software. Thus, the flexibility in changing indicia images or adding customized ad slogans is significantly increased.
Modern digital printing technology includes thermal ink jet (bubble jet), piezoelectric ink jet, thermal printing techniques, and LED and Laser Xerographic printing which all operate to produce images by dot-matrix printing. In dot-matrix ink jet printing individual print elements in the printhead (such as resistors or piezoelectric elements) are either electronically stimulated or not stimulated to expel or not expel, respectively, drops of ink from a reservoir onto a substrate. Thus, by controlling the timing of the energizing of each of the individual print elements in conjunction with the relative movement between the printhead and the mailpiece, a dot-matrix pattern is produced in the visual form of the desired indicia. However, in order to allow the printhead to produce the desired image, the entire image data are typically stored in an electronic non-volatile memory in a compressed manner, converted to binary data and downloaded and stored as a bit map in a temporary volatile memory, and then downloaded to the printhead driver. The indicia image contains both fixed and variable data. The fixed image data are the elements of the image that do not change. Examples of the fixed image data may include an indicia border, city and state of origin, meter number, zip code and other graphical information including advertising slogans. Variable image information is typically that image data which is changing on a per mailpiece basis such as the date, postage amount, or an encrypted value which is utilized to authenticate that a valid indicia has been printed. In order to print the full indicia, it is thus necessary to combine the fixed and variable data elements to create the required indicia for each individual transaction.
Postage meters utilizing digital printing technology typically combine the fixed and invariable image data into a complete bit map indicia image prior to printing. The image is conventionally combined by dedicating an electronic read-write memory (i.e. random access memory (RAM)) for use as temporary storage during the image element gathering stage. That is, while image data for the fixed and variable data are stored in a non-volatile memory (NVM), when an individual transaction takes place the postage meter microprocessor obtains the required variable and fixed data elements for that transaction from the non-volatile memory and combines and downloads the required variable image data with the fixed image data into the electronic read-write memory as a bit map of the actual entire indicia to be printed, thereby using the RAM as a temporary storage of the bit map image. The microprocessor then downloads the bit map image to the printhead for printing. However, since the variable image data changes from mailpiece to mailpiece, the microprocessor must edit the bit map image for every indicia printed. Editing an indicia bit map image significantly affects the performance and cost of the postage meter since it 1) takes time to do thereby reducing throughput, 2) requires a large amount of RAM, 3) demands the use of a high speed microprocessor and 4) requires a large amount of additional code and associated memory to perform the editing function.
European Patent Application 0 578 042 attempts to solve some of the problems addressed above by combining the fixed and variable image data during the printing of individual columns of the image. However, the apparatus of the aforementioned European Application still utilizes a RAM as a temporary memory for building a bit map image of the entire fixed image for each transaction prior to printing. Since the amount of fixed image data is typically much greater than the variable image data, a great deal of editing on a mailpiece by mailpiece basis is still required by the microprocessor and the need for a large amount of RAM and a high speed microprocessor still exists.
What is needed is a postage meter having a bit map image generator which builds an entire indicia image on a column-by-column basis in real time as printing occurs thereby 1) eliminating the need for editing and the temporary storage of the image in RAM, 2) freeing the microprocessor to perform other functions, and 3) increasing the throughput capability of the postage meter. Moreover, by eliminating the need for the RAM and fleeing the microprocessor to perform other functions, a high speed microprocessor is not required resulting in a reduced cost associated with implementing digital printing technology in a postage meter.